Baltimore County's longtime historian is widely known as a 'walking archive' Peerless authority: One Baltimore County official says John McGrain 'has got a lock on historic issues.'

To John W. McGrain, the lichen-green stones -- overgrown by trees and vines but with squared edges that nature never cut -- read like a building plan of the old cotton mill that once operated on the site.

"This is the mere stump of the mill that was here," Mr. McGrain said, snapping photographs of the granite ruins of Gray's Mill -- built about 1820 at the town of Thistle on the Patapsco River just downstream from Ellicott City, and finally abandoned in the 1930s.

"It was a huge building," said Mr. McGrain, 64, the Baltimore County historian, comparing the ruins to old stereopticon pictures with debris from an 1868 flood still visible.

"John is the authority on mills in Maryland -- the whole state, not just Baltimore County. I call him when I need information on mills in Frederick County," said Janet Davis, historian in that county's Planning and Zoning Department.

The mills that dotted Maryland rivers from Colonial times to the 19th century remain his first love, but Mr. McGrain's broad knowledge of, and passion for, history goes far beyond them.

As executive secretary of the county's volunteer, 15-member Landmarks Preservation Commission, formed in 1976, the Baltimore native has been instrumental in making historic preservation respectable and effective, said P. David Fields, former county planning chief and now community conservation director.

When development proposals threaten historic sites or buildings, the commission "has legitimized the process of community involvement and opposition. It became OK for people to object to things," Mr. Fields said.

"When John testifies [before county agencies], he goes without questioning and without peers. He's got a lock on historic issues," said Arnold F. "Pat" Keller III, the present planning director.

Mr. McGrain's inquiring mind and the acquisitive instincts of a pack rat have produced a near-encyclopedic knowledge of old buildings, their construction and later changes, and the people who lived or worked in them.

When he's not hunched over the desk in his tiny Courts Building office, crammed with the files and photographs of Baltimore County's past that he has accumulated since the early 1960s, he is out inspecting and photographing everything from near-forgotten ruins to the finest old homes.

Or he might be holed up in the county land records office, the Maryland or Baltimore County Historical Society or at the Hall of Records in Annapolis, studying old deeds, records of lawsuits or newspaper ads of auction sales which frequently contain detailed descriptions of buildings.

Another time he might be thumbing through boxes of old postcards at a flea market for pictures of long-demolished houses and other buildings.

As the county's historic watchdog, Mr. McGrain reviews development plans for their potential impact on sites listed with the county and the Maryland Historic Trust. On his recommendation, the landmarks commission might decide whether or not to oppose any such plan.

The county has listed for protection 120 sites and seven historic districts, while the county and the trust together have identified 2,500 sites of historic interest including homes, barns, bridges, chapels and schoolhouses.

Mr. McGrain's counterparts in other area planning departments consider him an invaluable resource. "When I need some information, chances are he has something stored away and he's always ready to share it," said Anne Arundel County's Donna Ware.

The state of historic preservation in Baltimore County is "pretty good" and getting better, Mr. McGrain said, adding: "There is plenty of interest in preservation and public support against developers and other white-collar criminals who would destroy historic places."

But developers, he added, have begun "to actually see the commercial possibilities in old buildings."

For all his travels and studies, Mr. McGrain says his work is nowhere near complete. "Baltimore County has a very rich history, and there are a lot of early settlements and Indian sites yet uncovered," he says.